Section VIII UW-50 WELD EXAMINATION 4

[spike]

UW-50 requires that on welded vessels to be pneumaticaly tested in accordance with UG-100 that some welds be examined for cracks.

If the vessel is to be hydrostatically tested would welds be subject to examination for cracks? Apparently not.

Does anyone know the logic behind this?

 

[metengr]

No. Pneumatic testing is not the same as hydrostatic testing. The reason for UW-50 NDT is to assure that external welds are examined in addition to the vessel base material and full penetration welds by pneumatic testing.

Hydrostatic testing places the entire pressure vessel boundary and welded attachments under local tensile stress. Thus, you can take credit for a more comprehensive examination using hydrostatic testing.

 

[deanc]

Hmmmmm-think this is more of a safety thing. The NDE is required before the final test. Lets not have a nozzle blow off,heh?

In any case see Code Case 1518.

 

[JoeTank]

The additional NDE for nozzle cracks is to assure that no cracks exist before one embarks on the much risker pnuematic test. This additional NDE is done in recognition that a pnuematic test has much greater stored energy involved that a standard pnuematic test. Also, nozzle welds are the man-made components which results in a higher defect rate, hence higher risk of failure. Overall it's a safety thing.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com